Firstly, questions of this nature should be asked in the Oddworld Q&A thread, otherwise they tend to clutter up General Discussion. As for your answers...
1. The games are all pretty much the same. The American version of MO has slightly different 'number graphics' (that is, the font of the amount of Spooce shown above Abe and Munch), and some of their 'Healt Ups' are actually SoBe Vendos.
2. Abe is the hero of the Quintology, so all that Quintology games will feature him. His story will only become resolved (or possibly not...) at the end of the Quintology. Now, outside of the Quintology Abe doesn't have to take such a pivatol role in the game. In fact, he's not appearing in Steef at all.
3. Pardon me?
4. Steef and the next two Oddworld games following it will be Xbox Xclusive, just like Munch. They will not be ported or recreated on any other console until their liscence runs out, which is going to be some time away. However, there is a Munch's Oddysee coming out on GBA soon-ish.
4. We will visit Meeches and see how they lived, although it's unknown whether they will actually be resurrected from apparent extinction, or whether we will see them in flashbacks. Hand of Odd was, at some point, going to be based in Oddworld's past, so we might have seen Meeches around back then.
Now remember the Q&A thread.
EDIT: Dang you, Xavier, dang you to Acherontan! You beat me.